Date of Award
Masters of Science
William B. Martin, Jr.
This thesis presents methods for preparation of sterically hindered organic acid esters. The secondary- and tertiary-butyl esters of 2,2’ dimethylpropanoic acid (pivalic acid, neo-pentanoic acid, or trimethyacetic acid) were prepared by suggested methods. The best method proved to be that suggested by Bochkova, Proskuryakov, Pirozhkoc and Eidus, where the esters of neo-acids are prepared through their respective acid chlorides. In the case studies in this thesis, the acid chloride of neopentanoic acid (pivaloyl chloride) was reacted with secondary or tertiary-butyl alcohol. Kinetic studies of the saponification of secondary-butyl pivaloate were made at various temperatures, and from the data obtained, the kinetics for the reaction were determined to be second order at 33°C, 43°C and 53°C. The reaction rate constants (k) for this secondary ester were determined to be k33°C = 1.8x10-4 liter (mole minute)-1 and k53°C = 8.63x10-4 liter (mole minute)-1. From a plot of the log of reaction rates constants versus corresponding reciprocal temperatures, the activation energy was determined to be approximately 15.5 Kcal (mole)-1. However, at 109° a kinetic study seemed to indicate first order reaction kinetics for secondary-butyl pivaloate. This suggests the reaction mechanism Bi4 for the gas phase pyrolysis of esters or the BAL mechanism for stable carbonium ions. The rate constant was determined to be 3.4x10-3 minutes-1. A similar study is yet in progress using the tertiary-butyl pivaloate. The rates of reaction are much slower than those of the secondary reactions and seem somewhat less temperature dependent. The optically active (+) secondary-butyl pivolate was prepared from the (+) secondary-butyl alcohol via the acid chloride. This ester has a specific rotation of [∝]D26 = 26.53°. When saponified at 53°C an attempted kinetic study by optical activity of this ester showed inversion of observed rotation. Vapor phase chromatography suggests no beta-ethoxyethyl secondary-butyl ether formation. Accordingly, V.P.C showed the presence of secondary-butyl alcohol. This indicates the BAL2 mechanism, since this appears to be the only logical way to explain product of inverted rotation given the V.P.C results.
Walrath, George A., "Mechanisms of saponification of sterically hindered esters by optical activity and kinetic studies" (1977). Honors Theses. 1861.